Petty argument (8)
'petty argument' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tiff that I've seen before include "Mild quarrel" , "Minor argument" , "Lovers' row" , "Minor squabble" , "Row; argument" .)
(Other definitions for squabble that I've seen before include "Have a minor row" , "Bicker" , "Petty row" , "Quarrel in petty or noisy way" , "Quarrel about petty points" .)